This invention relates to an ion selective electrode and a flow type ion sensor using the same, capable of selectively measuring specific ion concentrations.
More specifically, it relates to an ion selective electrode and a flow type ion sensor using the same which are excellent in the adhesion of an ion sensitive membrane, and thus indicate stable potentials, and have a prolonged life time.
The ion selective electrode can characteristically accomplish a selectivity quantitative determination of specific ion concentrations in a liquid, and it has heretofore been used in many fields such as monitoring of specific ion concentrations and water analysis.
For example, in the case that an ion selective electrode to be used is a cation selective electrode, a relation between an activity a+ of an aimed cation and a potential E indicated by the cation selective electrode is represented as follows: EQU E=E.sup.0 +2.303(RT/zF)log a+ (1)
Further, in the case of an anion selective electrode, a relation between an activity a- of an aimed anion and a potential E indicated by the anion selective electrode is represented as follows: EQU E=E.sup.0 +2.303(RT/zF)log a- (2)
As understood from them, a logarithm of the activity and the potential are in a proportional relation, therefore the activity of the aimed ion can easily be obtained from a measured potential value.
In the aforementioned formulae (1) and (2), R is gas constant, T is absolute temperature, z is an ion value, F is Faraday constant and E.sup.0 is a standard electrode potential in a system.
If the ion selective electrodes mentioned above are used, a measurement of the potentials will easily permit the quantitative determination of the ion concentrations in an extensive range. Further, if the ion selective electrodes having the small-size electrode members are employed, the determination will be possible even for a small amount of a sample. As is definite, such ion selective electrodes are convenient, therefore they are often utilized of late in a medical field, particularly for the measurement of various ions such as Na.sup.30, K.sup.30 and Cl.sup.- present in a blood.
Moreover, a variety of analytical instruments each in which the aforementioned ion selective electrodes are used has actually been devised, and their uses are now getting expensive as analytical instruments for bloods and the like in the medical field.
Of these ion selective electrodes, ones having simple structure are popular particularly because of easiness of its manufacture, handling and maintenance, in which simple structure each ion sensitive membrane is formed directly on a metal member without any internal electrolyte solution.
Additionally, as a method of successively measuring the respective concentrations of plural kinds of ions in the liquid to be measured, a so-called flow cell system is known in which a plurality of ion selective electrodes is disposed in parallel across a flow passage of the liquid sample, and electrical signals from the respective electrodes are then analyzed.
Moreover, in recent years, there has been developed a flow type ion sensor in which ion selective electrodes without any internal electrolyte solution are integrally coupled in a flow cell system.
In this flow type ion sensor, the passage for the liquid to be measured is defined by electrode surfaces of a plurality of ion selective electrodes, therefore it is feasible to render its structure small-size and multifunctional, further, advantageously a less amount of the liquid to be measured suffices to accomplish the ion analysis.
In such a flow type ion sensor, each pipe of a noble metal such as gold or silver is coated with an ion sensitive membrane.
However, the flow type ion sensor comprising such noble metal pipes is costly, as a great amount of the noble metal material is used, and the adhesion between the metal and the ion sensitive membrane is bad, thereby disadvantageously shortening its life time.
For this reason, another electrode has been suggested in which a plastic plate is provided with a through hole for allowing a liquid sample to flow therethrough, and a metallic thin membrane is mounted on a part of the inner surface of the through hole, instead of the metal pipe.
With regard to this flow type ion sensor including the plastic plate, it can be inexpensive because of a less metallic material, and not only the metallic surface but also the plastic surface adjacent to the above metallic surface portion is extensively coated with the ion sensitive membrane, whereby the improvement in the adhesion of the ion sensitive membrane can be expected.
Materials for the plastic plate which have heretofore been used for such a purpose include an acrylic resin, a phenolic resin, an epoxy resin and the like.
However, the adhesion between the plastic plate and the polyvinyl chloride resin membrane of an ion sensitive membrane material is not as good as expected. As a result, peeling of the membrane often will occur, so that the liquid to be measured will be contiguous to the metallic plate to bring about a short, and obtained potentials will thus be unstable and the life time of the ion sensor will be noticeably shortened.
An object of the invention is to provide an ion selective electrode and a flow type ion sensor using the same which are excellent in an adhesion of an ion sensitive membrane, and can thus give stable potentials, and a prolonged life time.